The present invention relates to an apparatus for installing nut inserts to a workpiece, the workpiece having a first side and a second. Usually the first side is a visible side and the second side is a blind side, meaning there is no access to the second side. More particularly, this invention relates to a modified installation tool which reduces incidents of cross-threading of the nut insert and/or damage to the installation tool.
It is known to use threaded rivet nuts, threaded inserts, and threadable inserts (generally, “anchor devices”) as anchors for threaded fasteners in a number of different applications, including thin wall applications, such as sheet metal, which may be too thin to be tapped with threads. In many such cases there is access only to one side of the workpiece. In general, the workpiece is drilled or punched and the anchor device is placed within the resulting hole. The anchor device is either threaded onto a threaded mandrel of the installation tool and placed within the hole by the installation tool, or the threaded mandrel is made up onto the threads of the anchor device after the anchor device has been placed in the hole. When the installation tool is activated, a portion of the anchor device on the blind side of the workpiece, such as a sleeve portion, is deformed to create an enlargement or bubble which prevents removal of the insert from the hole. After the installation tool is removed, a threaded fastener may be inserted into a threaded portion of the insert.
Installation tools for setting nut inserts, particularly in blind applications, are generally known. These tools generally comprise a tool body from which extends a mandrel having external threads. The mandrel typically extends through a nose piece which is connected to the front of the tool body. Rotational means are operationally connected to the rear of the mandrel for rotating the threaded mandrel to make up the threaded mandrel within the nut insert prior to deformation of the sleeve portion. The threads of the mandrel are made up into the threads of the nut insert until a flange on the end of the insert abuts the front end surface of the nose piece. If not already placed within an aperture of the work piece, the insert is thereafter placed within the aperture until the flange abuts the first side of the workpiece.
A linear force is applied to the mandrel by partially pulling the mandrel into the tool body with reciprocation means. The linear force applied to the insert causes the sleeve of the insert to plastically deform, such that the resulting enlargement or bubble is larger than the diameter of the aperture, preventing withdrawal of the insert from the aperture. Examples of such tools may be found in U.S. Pat. Nos. 4,070,889; 4,368,631; 4,612,793; 4,574,612; 5,605,070; and 6,272,899.
On occasion, the threads of the insert are cross-threaded as the male threaded mandrel is inserted into the female threaded insert. Cross-threading can occur with a threaded insert when the threaded mandrel is engaged with the female insert and the threads are not properly aligned when the threads of the mandrel and the threads of the insert first engage. If the threads of the mandrel and the threads of the insert are not properly aligned at the start, the external thread tends to cross over the crest of the internal thread which can produce deformation of the threads and can also cause binding of the mandrel and insert before the desired makeup of the mandrel into the insert is achieved. Unless the mandrel and nut insert are manually realigned at this point, the external thread will wedge against the internal thread and prevent the proper makeup of the mandrel into the nut insert and/or cause damage to the threads of either the insert or the mandrel.
It has been found by the inventor herein that in addition to improper alignment, another cause of cross-threading is that the threads of the insert adjacent to the opening, including the root thread, can be damaged by the tip of the mandrel as the mandrel is inserted into the opening of the insert by the operator or operating machinery. The tip of the mandrel may impact the crests of the threads of the insert as the tip is inserted into the opening of the insert. With the existing installation tools, there is little give by the mandrel, such that the resulting impact load is absorbed almost entirely by the threads of the insert.